With reference to FIG. 1, remotely operated underwater vehicles (ROV's) 101 are, widely used by industry and science for unmanned undersea work tasks. Some ROVs 101 require an electromechanical cable connection (tether) 105 to the surface for communications and power which are typically located on a boat 109. These cables 105 are thick and heavy because they contain the required electrical conductors to provide power to the ROV 101. As the ROV 101 moves away from the boat 109, the tether 105 is released from a tether storage device 111.
In order to control the movement, the thrust 115 produced by the propulsion device 113 on the ROV 101 must be greater than the tension in the cable 105. The tension on the cable 105 is generated by drag on the cable due to the movement of the cable 105 through the water. The total tension can be proportional to the wetted surface area of the cable 105. Thus, more tension exists in the cable 105 and more thrust is required as the ROV 101 travels farther from the ship 109. This can be problematic because cables 105 can be damaged when the tension exceeds a certain force. What is needed is a system for preventing over tensioning of the cable 105.